Kirill Dmitriev, the Kremlin’s top economic envoy, arrived in the United States with holes in his sails and no wind to push him forward. He was a man on a desperate mission. A phone call between Sergei Lavrov, Russia’s foreign minister, and Marco Rubio, the US secretary of state, had not gone well. The meeting between Vladimir Putin and Donald Trump, expected to take place within two weeks, was shelved. The US president had finally lost patience with his Russian counterpart’s refusal to support a ceasefire in Ukraine. On Wednesday, he slapped Moscow’s largest oil firms with crippling sanctions. With...